Yet another interesting addition to the upcoming Rails 4 beta, the not method allows to do exactly the opposite of a where method without having to use SQL syntax. Sadly, two methods for LIKE and UNLIKE didn't make the cut.

Standard Rails error pages are a bore and not very easy to digest for beginners, this new gem by Charlie Somerville adds some nice styling to them, allows you to jump from the call stack to the source code of the relevant files with syntax highlighting and it even offers an inline REPL (Read-Execute-Print-Loop) to use as a debug console when things go wrong.